The X11 window system will display a login window which has user identification and password files. If the screen is black you may have to move the mouse or press a key on the keyborad to exit the screen save mode. First enter your userid and then your password each terminated with the return key. This will start an automatic login procedure (see OSF/Motif manual for customising the widow manager). In case you don't have an account on the systems you should contact the System Manager (room 220/2).